The Applicant has a long history of experience in the field of fire and explosion detection and control in processes involving agricultural dusts, pharmaceutical dusts, propane/air mixtures and other combinations characterized by a relatively long initial period of slow fireball growth prior to the "explosion" reaching its maximum rate of pressure increase and which are referred to as deflagrations. The equipment with which he is most familiar is not able to control the ignition (detonation) of high explosives, as, comparatively, they do not go through an initial period of relatively slow growth before reaching their maximum rate of pressure rise. The primary difference is that materials involved in a deflagration (slow initial rate of pressure rise) must seek out oxidizers contained in the air, and this process is accelerated as the fireball increases in surface area. In the case of detonation, the oxidizer is already mixed with the fuel, so the pressure rise is achieved almost instantaneously.
This invention then is directed to the control of a deflagration-type of "explosion" but this requires use of materials that will detonate to achieve suppression of a developing fireball, because the "relatively slow fireball growth rate" of the deflagration involves only milliseconds, the blink of an eye, and it has a head start on the counter measures.
The invention also considers at least one particular condition. In certain installations, it is often necessary to protect maintenance personnel that may be working in the "rated or protected" area, referred to as a hazardous area, from spurious discharge of explosion-response devices and certain, in-use, methods include mechanical blocking devices. These may cover those devices that utilize high discharge pressures in the range of 500 psig to 900 psig, where accidental discharge may create, not only a "scary" but dangerous situations, to maintenance personnel. With the Applicant's devices which utilize a low, 200 psig pressure level, an accidental discharge may be more "scary" than dangerous but this is still a concern of maintenance personnel.
It is well known in the field of explosives that detonators, including blasting caps, must have their connecting wires shorted to each other in order to prevent spurious discharge. This is necessary because wires serve as antenna which can pick up energy from various sources such as radio transmission waves or adjacent wires carrying alternating current. The result could be that sufficient energy is fed to the low resistance detonator bridge circuit that their coating of pyrotechnic material ignites, setting off the explosive train that is common to all detonators.
Applicant's invention provides a mechanism to remotely control the position of the moveable leaf of a reed switch to shift the same from an On, energy transmitting position, to an Off, short-circuiting position. Once so switched, an OSHA lockout can be coupled to prevent an accidental reestablishing of the circuit. During this period of disconnect, the invention may include a latching device to prevent release of air from a pressurized air source which could independently expel suppressant from the device.
The remote control basically consists of a rotatable magnet which is electrically and mechanically isolated from the switch, the switch and associated detonator being housed in a first housing section which contains a quantity of suppressant material which is discharged from the housing upon explosive discharge of the detonator. Such remote control magnet is mounted for rotation within a second housing section and has an external operating member such as a simple knob. To indicate to the person responsible for disarming, the knob is designed and selected to give a physically readable showing of magnet and thus switch position. Simultaneously with switch shifting, both a local, visual and a remote, visual indicator means is actuated to verify the switch position and condition to a nearby and remote location accessible to maintenance personnel and to remote locations such as a control rooms in which the fact of disarming the release device may be monitored.
When the unit is rearmed and fireball growth is sensed, the detonator discharge is initiated and the resulting explosion opens certain frangible portions of the housing to dispel suppressant with pressurized air also being simultaneously introduced to the housing to deliver the suppressant into the rated or process area.
It is therefore an object of the applicant's invention to provide a remote disarm mechanism for explosive equipment which includes structure for positively shifting the leaf of a detonator controlling reed switch into an Off, short-circuiting position without making electrical or mechanical contact with the reed switch.
It is a further object of the applicant's invention to provide a remote disarm mechanism for a detonator bridge switch which will provide a visual indication of operative condition of the detonator bridge control switch as well as a local and remote indication of such condition.
It is a further object of the applicant's invention to provide a remote disarm mechanism for a detonator bridge switch which provides accommodation for the attachment of an OSHA lockout device to a control knob thereof to prevent movement of such control knob and thus disarm mechanism.
It is still a further object of the applicant's invention to provide a remote disarm mechanism for a control switch of a detonator bridge circuit which includes the introduction and positioning of a controlling magnetic field to position such switch in an armed or disarmed position and wherein the means for controlling such field are remote from said switch or other mechanism of the explosive equipment.
It is still a further object of the applicant's invention to provide a containing latch against movement of a mechanism for release of pressurized air into the suppressant containing section of the structure, said latch being engaged simultaneously with the device that is activated with the shifting of the control switch.
It is still a further object of the applicant's invention to provide a pressure air source opening mechanism which is responsive to detonation of the explosive within the extinguishant container to open the same upon such detonation, with means to simultaneously control the same to prevent actuation of such opening mechanism when the detonation device is switched to an Off or Inactive position.
These and other objects and advantages will more fully appear from a consideration of the accompanying drawings and disclosure.